In many countries, governments are requiring manufacturers to reduce the amount of emissions which are expelled from small internal combustion engines. Manufacturers of internal combustion engines are therefore constantly developing new ways to reduce emission levels.
One source of unwanted emissions develops when the fluids, (typically conventional motor oil), that are used to lubricate the valve stems and valve guides within an internal combustion engine escape from the engine. In many engines, the lubricating fluid escapes past the valve seals, through the intake and the exhaust valve guides, and thereafter enters the intake and exhaust manifolds through the valve ports.
The level of unwanted exhaust emissions increases when the lubricating fluid escapes from the exhaust valve guide because the lubricating fluid is then expelled from the engine along with the rest of the emissions. The level of unwanted emissions also increases when the lubricating fluid escapes past the intake valve guide. The lubricating fluid that escapes past the intake valve guide enters the combustion chamber. Since the lubricating fluid is not readily combustible under these conditions it is not completely burned, and as a result the lubricating fluid is expelled from the engine as emissions. Carbon deposits are also formed on and around the intake valve head in addition to the inner surfaces of the internal combustion chamber. These deposits absorb some of the hydrocarbons contained within the air/fuel mixture that is input into the combustion chamber. The hydrocarbons are absorbed into the deposits during the compression stroke of the engine, causing the absorbed hydrocarbons to escape combustion. The absorbed hydrocarbons are then released during the exhaust stroke, resulting in increased levels of unwanted emissions.
Valve seal assemblies are commonly installed on the cylinder head in an engine having an overhead-valve configuration, and in the engine block on an engine having a side valve configuration. The valve seal assemblies are usually located on the end of the valve guide that is farthest from the combustion chamber. Conventional valve seal assemblies also include a resilient seal element that is compressed against the valve stem in order to prevent most of the lubricating fluid from travelling past the sealing element.
Valve seal assemblies are commonly installed over protruding portions of valve guide inserts. Conventional valve seal assemblies are also inserted into counterbores. The valve seal assemblies typically include a bottom surface that is sealingly engaged with the bottom surface of the counterbore. The bottom surface of the counterbore does not provide a sufficiently smooth finish capable of satisfactorily sealing the valve seal assembly with the counterbore due to the presence of jagged cutters on the cutting tool used to create the bottom surface of the counterbore.
One drawback associated with using known valve seal assemblies is the design of the lips in the sealing elements. Conventional lip designs typically allow some lubricant to leak past because the seal assembly is located on the end of the valve guide which is farthest from the combustion chamber. The valve seal assembly must allow some amount of lubricant to leak past the sealing element or the valve stem and valve guide will not receive any lubricant. Once the lubricant enters the valve guide it can travel along the length of the valve stem and valve guide until it enters the valve port. As stated previously, when the lubricating fluid passes through the valve ports, the level of unwanted emissions increases.
Another drawback of known valve seal assemblies is that the seal element is positioned too close to the valve guide. During operation of the engine, the valve stem of the valve becomes damaged with notches and burrs as it reciprocates within the valve guide. When the notches and burrs travel back and forth across a lip on the sealing element, the lip is damaged resulting in reduced operating life and effectiveness of the valve seal assembly.